1. Field of the Invention
The present invention relates generally to medical treatment of cancerous tissue, and, in particular, relates to the medical treatment of cancerous tissue by use of radiation, and, in greater particularity, relates to medical treatment of cancerous breast tissue by a source of radiation using brachytherapy.
2. Description of the Prior Art
Various techniques have been developed to treat tumors in the body. In general, the use of radiation as a means to reduce or eliminate malignancy has been known for many years. One of the major issues in all of the techniques is the prevention of damage to healthy tissue.
The type of radiation treatment of malignant tumors most often performed involves directing a beam of radiation from a point external to the patient's body onto the area of the body in which the tumor is located, for the purpose of shrinking and ultimately destroying the tumor. This technique is known as “teletherapy” or external beam radiation therapy. Such treatment exposes normal healthy tissue to the high dosage of radiation in the beam and consequently subjects the normal tissue to potential injury.
In contrast to external beam radiation therapy, brachytherapy is a method of radiation treatment of cancerous tissue in which the radiation source is placed in or near the cancerous tissue. Brachytherapy treatment permits administration of a higher radiation dose to the tumor with better sparing of surrounding normal healthy tissues.
Brachytherapy came into use as a treatment tool for cancer soon after the discovery of radium by Marie Curie in 1898. Goldberg and London used it for the treatment of facial basal cell carcinomas in 1903 with surface applicators.
Brachytherapy can be applied to cancer either by permanent implantation or by temporary application of removable sources. A variety of radionuclides and methods for permanent implantation have been developed.
Permanent implantation results in the radioactive sources, or seeds, being left in the body in perpetuity, delivering their radiation dose until the radioactive material in the source has completely decayed away. This is not desirable in many cases.
Temporary brachytherapy is a process whereby the radioactive sources are placed into the body, usually using an applicator, such as a needle, catheter or other tubular apparatus, for a period of time to deliver the requisite radiation dose, and then the sources are removed. With this treatment modality, applicators are prepositioned in the patient. The sources are later temporarily placed within them. This procedure is known in the field as “afterloading.”
Originally, temporary brachytherapy was performed using a technique that became known as “Low Dose Rate Brachytherapy.” Using this technique, radioactive sources would be applied to provide a dose rate of 0.4 to 2 Gy/hour to the tumor. Using these techniques, treatment would take several days, during which period the patient would remain hospitalized. Low dose rate techniques utilized a variety of radioactive isotopes, including 125Iodine, 137Cesium, 198Gold and 192Iridium.
Later, a technique for “High Dose Rate Brachytherapy” was developed. In current practice, this high dose rate brachytherapy technique uses a source to provide dose rates in the range of 2-7 Gy/minute. This technique permitted the treatment to be performed in less than an hour, and without the hospitalization of the patient. These treatments are typically delivered in multiple fractions over several days or weeks.
This high dose rate brachytherapy method generally employs a highly radioactive source integrally attached to a driving cable, which together are known as a source assembly. This source assembly is typically delivered via a catheter or other applicator appliance through a natural cavity, duct or vessel of the body directly to the tumor site for localized irradiation. An alternative approach is to insert a closed-end needle directly into the tissue to be irradiated to create the channel for source delivery. This technique is less likely to expose normal healthy tissue to injury than if external beam radiation were used. One or more catheters, for example, may be implanted in the patient's body to provide a path from an external point to and through the tumor site, so that the interior of the tumor mass is accessible via the catheter(s). The radioactive source is then mechanically delivered by pushing the source by means of the attached driving cable through the catheter for localized irradiation of the tumor for a very short period of time, usually in the range of only a few minutes per treatment.
The high dose rate source is securely located at the end of the source assembly, the other end of which is attached to a controllable apparatus known as a remote afterloader, for advancement or retraction. Advancement of the source assembly through the catheter to the proper locations for treatment of the tumor is achieved by pushing on the driving cable portion of the source assembly by an electro-mechanical device (afterloader). The source is left in the selected positions for predetermined time intervals (programmed into the afterloader) deemed necessary to provide the desired treatment, and is then automatically retracted and returned to a shielded storage area within the afterloader.
The radiation from a brachytherapy source is emitted nearly isotropically from the source, i.e., of equal intensity in all directions. This is disadvantageous in certain circumstances where the source may be located near to critical normal tissue which needs to be spared from the radiation. A number of techniques have been presented to provide shielding around a portion of the radiation source to occlude, absorb, the radiation being emitted in unwanted directions.
One patent describes a x-ray source with moveable local shielding positioned to direct x-rays from the source through the x-ray transparent window to the selected site. This describes a shielding element to occlude a portion of the radiation emitted from the source, essentially leaving the radiation unobstructed in other directions.
Another patent discloses a radiation source upon a push rod that is inserted into a delivery lumen of a shaft. A radiation shielding component is situated near the radiation source to block radiation and is configured to allow radiation therefrom in a predetermined pattern. The shielding component may be composed of a metal or a radiation absorbing material of different density. The device may be used to treat tissue surrounding a body cavity or an intracorporeal site and would include a cavity filling member into which the radiation source with shielding is inserted for treatment. The radiation shielding may be tubular or partially tubular or be imbedded into the wall of the catheter. The radiation shield may be solid or liquid in nature. A further related patent discloses a shielding member being tubular in design and centered upon the radiation source. A window in the tubular structure allows the radiation to exit without shielding. The window has a predetermined shape so as to treat diseased tissues.
One patent application publication describes a directionally emitting radioactive source for brachytherapy wherein a shielding element occludes a portion of the radiation emitted from the source, essentially leaving the radiation unobstructed in other directions. A variation in the radiation dose is noted due to the limited ability to totally block the radiation by the shielding.
Several other patents disclose treating vessels such as arteries in the vascular system. Non-circular dose patterns are produced by an attenuator section having two semi-circular components or bands, tubular sections, placed together, wherein one subtends an angle of about 200 degrees and the other about 120 degrees.
Another patent discloses the treatment of a prostate through the urethra with a radiation source having metal tubular shielding. The urethra/prostate are dilated to move the urethra to a lower dose position. Multiple sleeves of different lengths, thicknesses, and materials can be used to adjust the dose patterns to lessen damage to tissue adjacent the prostate and the urethra.
Accordingly, there is an established need for a device for modulating radiation from a brachytherapy source for treating breast cancer, in particular.